409. Longest Palindrome

Description

Given a string s which consists of lowercase or uppercase letters, return the length of the longest

palindrome

 that can be built with those letters.

Letters are case sensitive, for example, "Aa" is not considered a palindrome.

 

Example 1:

Input: s = "abccccdd"
Output: 7
Explanation: One longest palindrome that can be built is "dccaccd", whose length is 7.

Example 2:

Input: s = "a"
Output: 1
Explanation: The longest palindrome that can be built is "a", whose length is 1.

 

Constraints:

• 1 <= s.length <= 2000
• s consists of lowercase and/or uppercase English letters only.

 

Solutions

Solution: Hash Map

• Time complexity: O(n)
• Space complexity: O(n)

 

JavaScript

/**
 * @param {string} s
 * @return {number}
 */
const longestPalindrome = function (s) {
  const builtMap = new Map();
  let result = 0;

  for (const char of s) {
    const count = builtMap.get(char) ?? 0;

    builtMap.set(char, count + 1);
  }
  for (let count of builtMap.values()) {
    const isOdd = count % 2;

    if (isOdd) count -= 1;
    result += count;
  }
  return result < s.length ? result + 1 : result;
};